1. Field of the Invention
The present invention relates to the use of selected anthraquinone colorants in phase change inks. In particular, the invention relates to phase change ink compositions that comprise the combination of at least one phase change ink carrier component and a compatible phase change ink colorant that comprises the reaction product of at least one oxy-substituted-9,10-anthraquinone compound with at least one monofunctional amine compound.
2. Brief Description of Art
Phase change inks in digital printing applications (also sometimes called solid inks or hot melt inks) have in the past decade gained significant consumer acceptance as an alternative to more traditional printing systems such as offset printing, flexography printing, gravure printing, letterpress printing and the like. Phase change inks are especially desirable for the peripheral printing devices associated with computer technology, as well as being suitable for use in other printing technologies such as gravure printing applications as referenced in U.S. Pat. No. 5,496,879 and German Patent Publications DE 4205636AL and DE4205713AL assigned to Siegwerk Farlenfabrik Keller, Dr. Rung & Co.
In general, phase change inks are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the printing media, they quickly solidify to form a predetermined pattern of solidified ink drops.
They are easy to use and safe. They can be easily loaded into the printer by the user, generally in the form of solid sticks of yellow, magenta, cyan and black ink having a solid consistency similar to children's crayons. Inside the printer, these inks are melted at an elevated temperature in a print head having a number of orifices, through which the melted ink will be ejected onto the desired substrate such as media like paper or an overhead transparency film. Alternatively, the melted ink may be transferred to a rotating drum and then transferred to the substrate. As the ink cools on the substrate, it re-solidifies into the desired image. This resolidification process, or phase change, is instantaneous and a printed, dry image is thus made upon leaving the printer, which is available immediately to the user.
These phase change inks contain no solvents or diluents that can lead to undesired emissions. In all, the use and specific design of the phase change ink addresses many of the limitations of more traditional ink and printing processes.
Furthermore, because the ink is in a cool, solid form at any time when the user can actually come in contact with the ink, and the ink is in a molten state only inside the printer (inaccessible to the user), it is generally safe to use. These inks also have long-term stability for shipping and long storage times.
The phase change inks generally comprise a phase change ink carrier composition, which is combined with at least one compatible phase change ink colorant. The carrier composition has been generally composed of resins, fatty acid amides and resin derived materials. Also, plasticizers, waxes, antioxidants and the like have been added to the carrier composition. Generally the resins used must be water-insoluble and the carrier composition may contain no ingredients that are volatile at the jetting temperatures employed. Also, these carrier ingredients should be chemically stable so as not to lose their chemical identity over time and/or under elevated temperature conditions.
Preferably, a colored phase change ink will be formed by combining the above described ink carrier composition with compatible colorant material, preferably subtractive primary colorants. The subtractive primary colored phase change inks comprise four component dyes, namely, cyan, magenta, yellow and black. U.S. Pat. Nos. 4,889,560 and 5,372,852 teach the preferred subtractive primary colorants employed. Typically these may comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, C.I. Disperse Dyes, modified C.I. Acid and Direct Dyes, as well as a limited number of C.I. Basic Dyes. Also suitable as colorants are appropriate polymeric dyes, such as those described in U.S. Pat. No. 5,621,022 and available from Milliken & Company as Milliken Ink Yellow 869, Milliken Ink Blue 92, Milliken Ink Red 357, Milliken Ink Yellow 1800, Milliken Ink Black 8915-67, uncut Reactant Orange X-38, uncut Reactant Blue X-17, and uncut Reactant Violet X-80 or those described in U.S. Pat. No. 5,231,135.
Colored resin reaction products such as those described in U.S. Pat. No. 5,780,528 issued Jul. 14, 1998, and assigned to the assignee of the present invention, are also suitable colorants.
Polymeric colorants have also been being utilized in preparing commercial phase change ink jet inks, as well as potentially for use in other applications, such as gravure printing, and other types of inks and coating applications where coloration is desired. For example, the specific class of polymeric dyes characterized by: (1) an organic chromophore having (2) a polyoxyalkylene substituent and optionally (3) a carboxylic acid or non-reactive derivative thereof covalently bonded to the polyoxyalkylene substituent, have been described in U.S. Pat. No. 5,621,022 (Jaeger et al.).
Anthraquinone dyes and pigments have also been employed as a chromogen for many applications where colorants are required. Furthermore, it is known to make many derivatives of anthraquinones for specific colorant applications. Yet, anthraquinones and their derivatives have some short-comings when used in phase change inks. For example, solubility and blooming problems arise when known anthraquinone dyes are used in phase change inks. They are believed to be caused by the planar nature of the molecules of these colorants. Aggregation of dye moieties can take place more readily when the dye molecules are planar in nature. This aggregation leads to solubility problems at the operating temperatures inside the printer. Furthermore, any unaggregated dye molecules will work their way to the surface of the hardened phase change ink stick, resulting in blooming problems. Furthermore, the manufacturing processes for making commercially available anthraquinone derivative dyes have several disadvantages (e.g., solvents are typically used in making such derivatives, thus requiring solvent recovery, and such processes also involve elaborate purification procedures). The present invention seeks to retain the known advantages of anthraquinone chromogens (i.e., wide variety of purple to cyan shades, outstanding lightfastness and thermal stability) while overcoming the solubility and blooming problems of the conventional anthraquinone colorants as well as eliminating the above-noted manufacturing disadvantages of their preparation.